The present invention relates to a coffee machine and to a method of operating the same.
Coffee machines are largely known. An example of such a coffee machine is described in EP-B1-443-054. The known coffee machine contains a brewing means in the form of a piston-cylinder unit, with the cross section of the brewing cylinder being closed by a brewing strainer arranged on the piston and with the upwardly oriented front side being closed by a water distributing sieve. The water distributing sieve is to ensure that the water will uniformly wet the entire cross-section of the brewing chamber, and the sieve is therefore provided with a great number of equally sized flow openings which are uniformly distributed over the entire area. During operation the ground coffee required is heaped in the removed state of the distributing sieve from a place above the brewing means onto the brewing strainer. In the attempt not to spill any ground coffee, the formation of a heaped cone is inevitably accepted. After the ground coffee has been introduced in metered amounts, the distributing sieve is again brought into its closing position and supplied with water which is uniformly distributed above the distributing sieve and then drips onto the ground coffee in a uniformly distributed manner over the entire surface of the distributing sieve. Although the heaped cone may be somewhat leveled off by floating ground coffee, such a leveling process can at best be observed at the end of the brewing operation.
It is a known fact among the experts that for an optimum exploitation of the ground coffee the latter should, if possible, be present in a layer of uniform thickness.
However, known possibilities of achieving such a layer require efforts so great, or are not suited for all types of coffee machines, that instead of the use of such constructions the disadvantages of a heaped cone have rather been accepted. For instance, DE-C2-38 29 417 shows a household coffee machine with an overhead filter chamber and a kind of lid whose bottom side has provided thereon projecting ribs. After the ground coffee has been filled in, said lid is installed and manually rotated whereby the ground coffee is leveled off by the ribs.
In the coffee machine according to DE-A1-33 16 157, water distributing sieve and brewing strainer are arranged in ring-like configuration and the plunger is provided with an upwardly projecting longitudinal section terminating in a cone tip by which the filling opening for ground coffee can be closed. Whenever ground coffee is to be supplied in metered amounts, the plunger is moved slightly downwards and the ground coffee is portioned onto the cone tip of the longitudinal section so that said cone tip acts as a distributing means for a desired ring-like distribution of the ground coffee. Said construction, however, cannot be used in all types of coffee machines and can also not ensure a uniform layer thickness in radial direction.
It is thus the object of the present invention to provide a coffee machine and a method of operating the same, in which it is possible to level off the ground coffee with constructionally very simple means for obtaining a layer of a substantially uniform thickness.
In an embodiment of the present invention, the ground coffee is leveled off by non-uniformly introduced water prior to or at the beginning of the brewing operationxe2x80x94a measure which is universally applicable in all types of coffee machines as water has to be introduced into every brewing means of a coffee machine, and which, on the other hand, can be realized in a constructionally very simple manner. Depending on the special type and/or the position and constructional design of the ground-coffee metering means, the water can be directed by the means of the invention in such a purposeful manner onto the place of the initially greatest thickness of the ground coffee, i.e. the tip of the heaped cone, that the cone is leveled off. A further great advantage of the development according to the invention follows from the fact that the ground coffee can thereby be distributed in a uniform manner at any rate, irrespective of the size of the respectively metered amounts of ground coffee.
Using traditional equipment, the range of the amounts of coffee which could be brewed with a single size of a brewing chamber, i.e. with one and the same diameter of the support surface, has been limited. It had to be ensured that the metered amount of ground coffee was at least so great that the heaped cone thereof substantially covered the whole support surface, i.e. the brewing strainer. If the amount was too small, an area of the brewing strainer around the heaped cone was exposed so that water could directly pass therethrough, which considerably impaired the quality of the finished coffee beverage.
By contrast, in a coffee machine equipped with the means according to the invention, it is ensured that even a small amount of ground coffee can be distributed over the whole support surface and that as a consequence the brewing water is always bound to pass through the ground coffee before it can flow out of the brewing means. It is therefore possible to cover a considerably larger range of brewing batch sizes with one and the same brewing means, provided that it is equipped with the inventive means, without any loss in quality.
The non-uniform introduction of water can be achieved either by varying amounts or by different pressures of the introduced water.
In one embodiment, the invention incorporates a guiding means, such as a sieve, and an optimum distribution of the water which is respectively adapted to the specific type of the coffee machine and to the way how the ground coffee is metered can be achieved through an expedient design of the size and/or the distribution of the flow openings.
The desired, purposefully non-uniform distribution of the water can also be achieved by a plurality of water supply lines.
If a plurality of supply lines are combined with a sieve, the two areas of the sieve can be supplied with water in a predetermined sequence, resulting in the desired direction of flow.
If the water guiding means is configured in the manner of conventional water distributing sieves, already existing coffee machines can also be retrofitted with the means according to the invention.